<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <input type="button" value="按钮" id="btn">
  <!-- <script src="user1.js"></script>
  <script src="user2.js"></script> -->

  <script>
    var btn = document.getElementById('btn');
    btn.addEventListener('click', function () {
      alert('hello world');
    })

    btn.addEventListener('click', function () {
      alert('hello itheima');
    })
  </script>

</body>
</html>
